On May 3, 1802, Washington D.C. was officially incorporated as the capital of the United States. This historic decision was rooted in the constitutional authority granted to Congress under Article I, Section 8, which empowers the federal government to exercise exclusive legislation over the District of Columbia.

Specifically, the Constitution states that Congress has the power to:

"To exercise exclusive Legislation in all Cases whatsoever, over such District (not exceeding ten Miles square) as may, by Cession of particular States, and the Acceptance of Congress, become the Seat of the Government of the United States."

This incorporation solidified Washington D.C. as the permanent seat of the federal government, a role it continues to fulfill today.

Source: Reason